The alpha angle is a radiological measurement proposed for the diagnosis and evaluation of surgical treatment in cam-type femoroacetabular impingement (FAI).
When initially described in 2002, Notzli et al. suggested that the pathological value was >50°.
According to one study, a value measured in an oblique CT reconstruction of the femoral neck has been thought to have a high discriminating capacity for the diagnosis of symptomatic cam-type femoroacetabular impingement where if a patient complains of hip pain and an alpha angle ≥57° is found on CT, strongly suggest that cam-type FAI may be the cause 2.
Measured on obliquely oriented radiographs. The Dunn projection of the hip is used.
Measured on oblique axial images as the angle between the orientation of the femoral neck and the margin of the femoral head.
- 1. Jacob L. Jaremko, Myles Mabee, Vimarsha G. Swami, Lucy Jamieson, Kelvin Chow, Richard B. Thompson. Potential for Change in US Diagnosis of Hip Dysplasia Solely Caused by Changes in Probe Orientation: Patterns of Alpha-angle Variation Revealed by Using Three-dimensional US. (2014) Radiology. 273 (3): 870-8. doi:10.1148/radiol.14140451 - Pubmed
- 2. Barrientos C, Barahona M, Diaz J, Brañes J, Chaparro F, Hinzpeter J. Is there a pathological alpha angle for hip impingement? A diagnostic test study. (2016) Journal of hip preservation surgery. 3 (3): 223-8. doi:10.1093/jhps/hnw014 - Pubmed
- 3. Mohamed R. Nouh, Mark E. Schweitzer, Leon Rybak, Jodi Cohen. Femoroacetabular Impingement: Can the Alpha Angle Be Estimated?. (2012) American Journal of Roentgenology. 190 (5): 1260-2. doi:10.2214/AJR.07.3258 - Pubmed